1. Field of the Invention
This invention relates generally to magnetic heads, and more particular to antiparallel (AP) pinned type spin valve (SV) sensors having ultra-thin freelayers.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An re MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR elementxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flow through the MR element Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Nixe2x80x94Fe) separated by a layer of non-magnetic material (e.g., Cu) are generally referred to as spin valve (SV) sensors manifesting the GMR effect (also referred to as the SV effect). In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO or Fexe2x80x94Mn) layer. The magnetization of the other ferromagnetic layer, referred to as the freelayer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In the SV sensor, the SV effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the freelayer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the freelayer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. IBM""s U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses an MR sensor operating on the basis of the SV effect.
FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and 106 separated from each other by a central region 102. A freelayer (free ferromagnetic layer) 110 is separated from a pinned layer (pinned ferromagnetic layer) 120 by a non-magnetic, electrically-conducting spacer 115. The magnetization of the pinned layer 120 is fixed by an antiferromagnetic (AFM) layer 125. Freelayer 110, spacer 115, pinned layer 120 and the AFM layer 125 are all formed in the central region 102 over a substrate 128. Hard bias layers 130 and 135 formed in the end regions 104 and 106, respectively, provide longitudinal bias for the freelayer 110. Leads 140 and 145 formed over hard bias layers 130 and 135, respectively, provide electrical connections for the flow of the sensing current Is from a current source 160 to the MR sensor 100. Sensing means (a detector) 170 connected to leads 140 and 145 senses (detects) the change in the resistance due to changes induced in the freelayer 110 by the external magnetic field (e.g., field generated by a data bit stored on a disk).
Another type of SV sensor is an antiparallel (AP) pinned SV sensor. In AP-pinned SV sensors, the pinned layer is a laminated structure of two ferromagnetic layers separated by a non-magnetic coupling layer such that the magnetizations of the two ferromagnetic layers are strongly coupled together antiferromagnetically in an antiparallel orientation. The AP-pinning method provides improved pinning for the ferromagnetic layer than is achieved with the pinned layer structure of the SV sensor of FIG. 1. This improved pinning increases the stability of the AP-Pinned SV sensor at high temperatures and enhances its performance in hard disk drives.
FIG. 2 shows a prior art AP-pinned SV sensor 200 comprising end regions 204 and 206 separated from each other by a central region 202. A freelayer 210 is separated from a laminated AP-pinned layer structure 220 by a nonmagnetic, electrically-conducting spacer layer 215. The magnetization of the laminated AP-pinned layer structure 220 is fixed by an antiferromagnetic (AFM) layer 230. The laminated AP-pinned layer structure 220 comprises a first ferromagnetic layer 222 and a second ferromagnetic layer 226 separated by an antiparallel coupling (APC) layer 224 of nonmagnetic material. The two ferromagnetic layers 222, 226 (PF1 and PF2) in the laminated AP-pinned layer structure 220 have their magnetization directions oriented antiparallel, as indicated by the arrows 223, 227 (arrows pointing into and out of the plane of the paper respectively). The AFM layer 230 is formed on a seed layer 240 deposited on the substrate 250. To complete the central region 202 of the SV sensor, a capping layer 205 is formed on the freelayer 210. Hard bias layers 252 and 254 formed in the end regions 204 and 206, respectively, provide longitudinal bias for the freelayer 210. Leads 260, 265 provide electrical connections for the flow of the sensing current Is from a current source 270 to the SV sensor 200. Sensing means 280 connected to leads 260, 265 senses the change in the resistance due to changes induced in the freelayer 210 by the external magnetic field (e.g., field generated by a data bit stored on a disk).
FIG. 3 is a more detailed depiction of a read head 300 having a spin valve (SV) sensor 302 of the AP-pinned type, which is described in U.S. Pat. No. 6,317,299 B1. This SV sensor 302 is generally formed over a first read gap layer 301. SV sensor 302 includes a nonmagnetic conductive spacer layer (S) 304 which is located between a freelayer structure 306 and an AP-pinned layer structure 352. Freelayer structure 306 includes freelayers (F) 314 and a nanolayer (NL) 316 with the nanolayer located between spacer layer 304 and freelayers 314 for increasing the magnetoresistive coefficient (dR/R) of SV sensor 302.
Freelayer structure 306 has a magnetic moment 318 which is directed parallel to the ABS from left to right as shown, or optionally from right to left. Magnetic moment 318 is rotated upwardly and downwardly by signal fields from the rotating magnetic disk. When the sense current (Is) is conducted through SV sensor 302 a rotation of magnetic moment 318 upwardly increases the resistance of the sensor and a rotation of magnetic moment 318 downwardly decreases the resistance which are processed as playback signals. A cap layer 320 is located on freelayers 314 for protecting it from subsequent processing steps.
AP-pinned layer structure 302 also includes first and second AP pinned layers (AP1 and AP2) 354 and 356 with an AP coupling layer 358 located between first and second AP pinned layers 354 and 356. First and second AP pinned layers 356 and 358 have first and second magnetic moments 360 and 362 which are antiparallel with respect to one another. Because of this relationship, AP-pinned layer structure 352 produces a net demagnetizing field which is less than that using a conventional pinned layer. SV sensor 302 is also located on a seed layer structure 322 where pinning layer 310 interfaces with a first seed layer 324 thereof.
Conventional thicknesses and materials of the layers of SV sensor 302 are 250 Angstroms of platinum-manganese (PtMn) for pinning layer 310, 20 Angstroms of copper (Cu) for spacer layer 304, 15 Angstroms of cobalt-iron (CoFe) for nanolayer 316, 45 Angstroms of nickel-iron (NiFe) for freelayers 314, and 50 Angstroms of tantalum (Ta) for cap layer 320. Conventional thicknesses and materials for AP pinned layer structure are 23 Angstroms of cobalt-iron (CoFe) for first AP pinned layer 354, 26 Angstroms of cobalt-iron (CoFe) for second AP pinned layer 356, and 8 Angstroms of ruthenium (Ru) for AP coupling layer 358. Seed layer structure 322 for SV sensor 302 includes 10 Angstroms of cobalt-iron-boron (CoFeB) for first seed layer 324, 30 Angstroms of nickel-manganese-oxide (NiMnO) for a second seed layer 326 and 30 Angstroms of aluminum-oxide (Al2O3) for a third seed layer 328 with the second seed layer located between the first and third seed layers.
Thinner freelayer structures are becoming necessary due to increasing areal densities. It is important that such freelayer structures maintain soft magnetic properties to provide low coercivities. Nanolayer 316, which is made of cobalt-iron, is necessary in SV sensor 302 for increasing the magnetoresistive coefficient (dR/R). Unfortunately when the thickness of freelayer 314 is decreased, nanolayer 316 increases percentage-wise at the expense of nickel-iron, which is very soft magnetically compared to cobalt-iron. Therefore, these thin freelayers possess large coercivities and intrinsic anisotropy. Control over thickness also becomes difficult for very thin freelayer structures. The use of AP-pinned freelayers, however, helps alleviate the latter problem.
Accordingly, what is needed is an AP-pinned type SV sensor which has a very thin freelayer structure with soft magnetic properties and high GMR.
A spin valve (SV) sensor has a cap layer made of tantalum; a copper layer formed beneath the cap layer; and a unique freelayer structure. The freelayer structure includes a first layer made of nickel-iron, a second layer made of ruthenium, a third layer made of nickel-iron, a nanolayer made of cobalt-iron, and a spacer layer made of copper adjacent the nanolayer of cobalt-iron. The first layer of nickel-iron is no greater than each one of the third layer of nickel-iron and the nanolayer of cobalt-iron. The nanolayer has a thickness of no more than 30 Angstroms. The net freelayer thickness, determined based on subtracting a thickness of the first layer of nickel-iron from a sum of thicknesses of the third layer of nickel-iron and the nanolayer of cobalt-iron, is less than 50 Angstroms. Advantageously, this thin structure provides a high magnetoresistive coefficient and soft magnetic properties.